Biomechanical finite element analysis of occipitocervical joint-zonular bone-occipital condyle-screw on the inclined plane

Biomechanical finite element analysis of occipitocervical joint-zonular bone-occipital condyle-screw on the inclined plane | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Biomechanical finite element analysis of occipitocervical joint-zonular bone-occipital condyle-screw on the inclined plane Nanjian Xu, Weihu Ma, Guanyi Liu, Renhai Feng This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8711284/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract Objective This study aimed to determine the biomechanical stability of C0-C2 vertebrae fixed by atlantooccipital joint-occipital condyle-slope screw fixation (AO-CO-C screws) using finite element analysis. Methods Using computed tomography images, a nonlinear intact three-dimensional C0-2 finite element model (FEM) was developed and validated. Six FEMs were reconstructed: intact model, unstable model, atlantoaxial fusion with C1 lateral mass screw and C2 pedicle screw fixation finite element model (Group A), occipital plate screw with C1 lateral mass screw and C2 pedicle screw fixation finite element model (Group B), transarticular atlantoaxial screw with C2 pedicle screw fixation finite element model (Group C), occipital-cervical screw with counter-odontoid peg-C2 pedicle screw fixation finite element model (Group D). Range of motion and maximum von Mises stresses were compared under flexion, extension, lateral bending, and axial rotation. Results Group D showed the greatest decrease in ROM(range of motion) with flexion, which was higher than that of the other techniques. The maximal von Mises stress on Group A and Group B showed the occipital condyle screw began contact with the occipital condyle bone, whereas Group C and Group D. Group C had maximal von Mises stress on the atlanto-occipital joint region; the maximal von Mises stress on Group A was located in the area where the occipital condyle screw began contact with the occipital condyle bone, whereas Group C and Group D had maximal von Mises stress on the atlanto-occipital joint region, and the maximal von Mises stress on Group B was located in the area of the bottom of the C1 lateral mass screw. Conclusion In this study, AO-CO-C screws fixation is the most stable technique. If surgeons have to use other fixation methods, they should be aware that additional fixation or postoperative immobilization may be required to achieve ROM restriction. Careful observation at the maximum stress site on the screw, including screw loosening, screw-bone interface disruption, or screw fracture, is necessary during follow-up imaging examinations(X-ray and CT scans)after occipitocervical posterior fixation. biomechanical finite element analysis screw fixation cervical spine Figures Figure 1 Figure 2 Figure 3 1. Introduction The junction between the occiput and the cervical spine is different in anatomy and function from the lower cervical vertebrae [ 1 ] . It is the most flexible segment of the cervical spine. Trauma, tumors, congenital malformations, and inflammation can all cause instability in the occipitocervical junction. Posterior occipitocervical fixation and fusion are commonly used to treat occipitocervical instability with good outcomes. Posterior occipitocervical fixation includes occipital and cervical side fixation. There are various techniques for cervical side screw placement, which provide reliable fixation. However, the anchoring points on the occipital side are limited to the occipital squama and occipital condyles. The occipital bone plate and screw system is currently the mainstream method for posterior occipitocervical fusion surgery, but factors such as the thickness of the occipital squama bone, the rich vascular network in the inner plate region of the occipital squama, can affect the fixation effectiveness and surgical risks. Additionally, for patients with partial occipital bone loss or severe osteoporosis after decompression surgery, occipital condyle screws can be used as an alternative. However, there are doubts about the possibility and stability of screw placement when patients also have congenital malformations. Some scholars have proposed the effectiveness of occipitocervical screw fixation through the atlantooccipital joint [ 2 ] . However, biomechanical studies on cadaver specimens have shown that screw fixation through the atlantooccipital joint combined with occipital bone plate fixation may be slightly inadequate in stability [ 3 ] . In 2021, our team designed and proposed the technique of posterior atlantooccipital joint-occipital condyle-slope screw fixation (AO-CO-C screws), with longer screw paths that traverse more cortical bone. The stability of the structure cannot be solely explained by the range of motion (ROM) limitations obtained from cadaver-based biomechanical studies. To understand the stability of the structure, it is necessary to study the stresses acting within the metal structure and utilize finite element models (FEMs) for analysis. In three-dimensional finite element models, various types of posterior occipitocervical fixation can be biomechanically tested and stresses can be compared within the instruments. Currently, there is limited research on posterior occipitocervical fixation using finite element methods. Therefore, this study intends to use the finite element method to analyze the influence of AO-CO-C screws on the biomechanical stability of C0-C2 and provide a theoretical basis for selecting surgical methods for occipitocervical instability. 2. Materials and Methods 2.1 Finite Element Model Establishment Separate normal C0-C2 finite element model, atlantoaxial instability finite element model, atlantoaxial fusion with C1 lateral mass screw and C2 pedicle screw fixation finite element model (Group A), occipital plate screw with C1 lateral mass screw and C2 pedicle screw fixation finite element model (Group B), transarticular atlantoaxial screw with C2 pedicle screw fixation finite element model (Group C), occipital-cervical screw with counter-odontoid peg-C2 pedicle screw fixation finite element model (Group D). (Fig. 1 ) 2.1.1 Establishment of Normal C0-C2 Finite Element Model Approved by the hospital’s ethics committee. Utilizing cervical spine CT imaging data of a 27-year-old female with no prior history of occipito-cervical diseases or traumatic fractures. DICOM data was imported into Mimics 21.0 software (Materialise, Belgium) to initially create corresponding 3D mesh models and export bone STL format model data files. Further processing was done using Geomagic 2017 software (Geomagic, USA) for surface optimization and feature modeling of cortical and cancellous bone, followed by assembly in SolidWorks 2017 (Dassault Systèmes, France) to simulate the normal state, and finally imported into Ansys 17.0 software (Ansys, USA) to establish the complete model. We performed a mesh convergence study to determine the optimal mesh size for both the instrumentation and the pelvis model. The study involved progressively refining the mesh and analyzing the resulting changes in deformation and stress values. The results demonstrated that a mesh size of 0.9mm provided stable and accurate results without significant changes in the outcomes. 2.1.2 Establishment of Atlantoaxial Instability Finite Element Model Building upon the normal C0-C2 finite element model, the atlantoaxial instability finite element model was created by eliminating the transverse ligament, alar ligament, and apical ligament using SolidWorks 2017 (Dassault Systèmes, France). 2.1.3 Establishment of Finite Element Models for Four Atlantoaxial Posterior Fixation Devices Four models of atlantoaxial posterior fixation devices were designed using SolidWorks 2017 (Dassault Systèmes, France), adjusting spatial positions and aligning them with the aforementioned atlantoaxial instability finite element model to create the finite element models for occipital fusion screw with C1 lateral mass screw and C2 pedicle screw fixation, occipital plate screw with C1 lateral mass screw and C2 pedicle screw fixation, transarticular atlantoaxial screw with C2 pedicle screw fixation, and AO-CO-C screw with C2 pedicle screw fixation. The fixation segments mentioned above are all in the C0-C2 region. The occipital fusion screw is inserted 2mm above the atlantoaxial joint, 5mm outward from the inner edge of the occipital condyle, with an inward angle of 22°and a head angle of 5°. The occipital steel plate screw fixation position is based on the method of Anderson et al. [ 4 ] , the transarticular atlantoaxial screw fixation position is based on Yan et al [ 5 ] ., and the atlantoaxial lateral mass screw and pedicle screw fixation is based on the method of Harms and Melher [ 6 ] . 2.2 Material properties, boundary conditions, and load conditions In Mimics software, material parameters are assigned to bones and implants based on the material parameter table, with screws and rods made of Ti-6A14V titanium alloy. We simulated the screws using a simplified cylindrical design. This choice was made to simplify computational load and focus on overall stability analysis. Ligaments are assigned values based on load-deformation curves, with specific ligament properties shown in Table 1 [ 7 – 8 ] . The motion of the bottom surface of C2 is restricted, and the contact characteristics between joints involve frictionless surface-to-surface contact. A vertical load of 40 N and a lateral bending, extension, and rotation moment of 1.5 N⋅m are incrementally applied to the upper surface of C0 to simulate the gravitational load on the head and the flexion, extension, lateral bending, and rotational movements of C0-C2 [ 9 – 10 ] . This study neglects the micro-motions between bones and screws, defining the contact between screws and surrounding bones as bonded contact. We used [tetrahedral(Solid186)] elements to model the bones and instrumentation in our finite element analysis. These elements were chosen for their suitability in capturing the complex geometry of the structures involved, particularly in relation to the bending and loading conditions applied in our study. Table 1 Material Properties Table Materials Elastic modulus Poisson’s ratio Cortical bone 11000 0.29 Trabecular bone 500 0.29 Articular cartilage 10 0.3 Anterior longitudinal ligament (C0-2) 10 0.3 Anterior atlantoaxial membrane (C0-1) 10 0.3 World behind the pillow (C0-1) 10 0.3 Sharp pointed ligament between teeth (C0-1) 38(1.88) Wing-shaped ligament 23(1.14) Cruciate ligament 16(0.79) Covering membrane (C0-2) 27(1.34) Anterior cruciate ligament (C1-2) 58(2.88) Posterior cruciate ligament (C1-2) 63(3.13) Joint capsule 176(8.73) Nuchal ligament 208(10.32) Internal fixation 180(8.93) 2.3 Observation indicators Compare the range of motion (ROM) of each model under different operating conditions to evaluate its stability; observe stress distribution cloud maps of four internal fixation devices after reaching static equilibrium under different conditions, and compare stress peak values and stress distribution characteristics. 3. Results 3.1 Validation of the complete finite element method In order to validate the finite element model, the range of motion (ROM) of the complete C0-C2 model was calculated and compared with the in vitro study by Takigawa T [ 11 ] . The ROM of the complete C0-C2 model is as follows: flexion/extension 29.5°±11.1°, lateral bending 4.3°± 4.6°, rotation 62.3°±13.0°. The ROM data from previous literature are very consistent with our research results. (Table 2 ) Table 2 Comparison of the ROM of the complete C0-2 model with the reference literature Forward bend + backward stretch Side bend Rotation Tomoyuki Takigawa etc. This study Tomoyuki Takigawa etc. This study Tomoyuki Takigawa etc. This study C0-C2 29.5°±11.1° 29.33° 4.3°±4.6° 11.6° 62.3°±13.0° 25.11° 3.2 Internal fixation stress distribution According to the screw fixation method of each type of internal fixation device, stress peaks inside the screws were observed at different locations (Fig. 2 ). The internal fixation stress peak of Group A is located in the region where the occipital condyle screw first contacts the occipital condyle bone. Stress peaks in the internal fixations of Groups C and D appear in the atlanto-occipital joint region. The stress peak of internal fixation Group B is located at the base of the lateral mass screw of C1 (i.e., the middle section of the entire fixation device). Group D’s internal fixation has the lowest stress peak in flexion conditions but has a higher stress peak in extension conditions; under lateral bending and rotation conditions, the stress peak is between the four types of internal fixation devices. In extension and lateral bending conditions, the internal fixation stress peaks of Groups A and B are lower than Groups C and D. In rotation conditions, the internal fixation stress peaks of Groups C and D are lower than Groups A and B. (Fig. 2 ) In forward bending, backward stretching, lateral bending, and rotation conditions, compared with the unstable cervical spine model, the ROM of the four groups of models all decreased by 80% (Fig. 3 ). In Group A, ROM decreased by 89.6%, 92.2%, 88.4%, and 86.0% in forward bending, backward stretching, lateral bending, and rotation conditions, respectively. Group B saw a decrease of 82.4%, 93.6%, 86.7%, and 84.3% in forward bending, backward stretching, lateral bending, and rotation conditions, respectively. Group C experienced reductions of 89.2%, 91.8%, 87.4%, and 85.5% in forward bending, backward stretching, lateral bending, and rotation conditions, respectively. Group D showed decreases of 89.2%, 90.0%, 92.0%, and 90.9% in forward bending, backward stretching, lateral bending, and rotation conditions, respectively. 4. Discussion Currently, occipitocervical fixation and fusion are widely used in the treatment of occipitocervical instability. Some scholars [ 11 ] have compared the biomechanics of various occipitocervical fixation techniques using range of motion (ROM) data in in vitro studies. However, due to the nature of cadaveric studies, each cadaveric model may have structural variations. Additionally, if experiments are conducted under different conditions for each model, the models themselves may deform, thus affecting the ROM data. In the case of finite element analysis, stress concentrations on the instrument can be measured without deformation of the model through repeated tests. In finite element analysis studies of occipitocervical fixation, there is still a lack of comparative research on four different fixation techniques. This study found that in flexion and extension conditions, Group C had higher stress peak values than Groups A and B, further confirming the inadequacy of stability in flexion and extension with occipitocervical screws. Compared to Group C, the stress peak values in Group D decreased significantly, especially in flexion conditions, even lower than Groups A and B. This indicates that compared to occipitocervical joint screws, AO-CO-C screws not only lengthen the trajectory but more importantly enhance stability. Our preliminary study found that the head inclination angle of AO-CO-C screws is approximately 50°, with an inward angle of about 18°, allowing the screw head to reach the front edge of the slope, crossing the center of gravity of the skull, providing effective support to the forehead. In addition, the direction of AO-CO-C screws is closer to the vertical plane, allowing the vector of skull gravity to be conducted along the long axis of the screw, and the 50mm lever arm is equivalent to the longitudinal connecting rod of occipital screws, compensating for the instability of occipitocervical screws in flexion and extension. In lateral bending conditions, the internal fixation stress peak values in Groups A and B are lower than in Groups C and D. In rotational conditions, the internal fixation stress peak values in Groups C and D are lower than in Groups A and B, but Group D is higher than Group C. This indicates that extending the lever arm can improve the rotational stability of internal fixation, but the impact of screws passing through the occipitocervical joint on rotational stability is more important. In addition, the addition of a cross-connecting rod during surgery can further enhance the rotational stability of AO-CO-C screws. The rigidity of the screws themselves, the length of the screw trajectory during insertion, and the number of cortical bone perforations are all important factors affecting the biomechanical stability of screws. Takigawa T et al. [ 11 ] believe that occipitocervical screws are too short to support the weight of the forehead and that patients with severe occipitocervical instability may still need additional anterior fixation. Yan Wangjun et al. [ 2 ] found that the trajectory length of occipitocervical screws is about 30mm, whereas the trajectory within the occipital condyle is even shorter. As a new occipitocervical internal fixation technique, AO-CO-C screws can achieve a trajectory length of over 50mm, providing a larger screw-bone contact interface compared to other screws. Additionally, in different fixation methods, stress peak values occur at different locations. The internal fixation stress peak of occipital condyle screws is in the region where the screw first contacts the occipital condyle bone. The internal fixation stress peak of occipital plate screws appears in the base area of the C1 lateral mass screw (i.e., the middle section of the entire fixation device). The internal fixation stress peaks of occipitocervical joint screws and AO-CO-C screws both occur in the occipitocervical joint region. AO-CO-C screws can penetrate through 2 layers of joint surface + 3 layers of cortical bone under the slope, far exceeding the 1 layer of cortical bone of occipital condyle screws and the 3 layers of cortical bone of posterior occipitocervical joint screws. For patients with severe osteoporosis or partial bone loss in the occipital region, AO-CO-C screws can provide greater resistance to screw pullout and reduce the failure rate of internal fixation. Therefore, based on the ROM, stress peak values, and stress distribution of each fixation device in this study, the structure of AO-CO-C screws is the most stable. Our study has several limitations. First, in finite element analysis, it is assumed that the screw is in full contact and fixed with the bone, which is not always achieved in clinical practice. Therefore, in the finite element model, this rigid bone-metal interface emphasizes the decrease in ROM after fixation. Our study analyzed the biomechanics of the occipitocervical region based on screw fixation, without considering bone fusion. Additionally, the impact of bone fusion on the stability of the occipitocervical region is not yet clear. To enhance the stability of the occipitocervical structure, we recommend increasing interbody bone grafts to improve stability. In conclusion, this study compared the biomechanical stability of four occipitocervical fixation techniques, which can help spine surgeons choose the appropriate surgical technique. For the strongest occipitocervical joint stability, this study recommends AO-CO-C fixation. If other fixation methods were chosen, we suggested increasing the duration of cervical support fixation postoperatively, closely monitoring and paying attention to the maximum stress points of the screw in imaging examinations (X-ray and CT scans), including screw loosening, screw-bone interface fractures, or screw fractures. Abbreviations AO-CO-C screws atlantooccipital joint-occipital condyle-slope screw fixation FEM finite element model, ROM=range of motion, CT=computed tomography Declarations Ethics approval and consent to participate The study was performed in accordance with the Declaration of Helsinki and was reviewed and approved by the Ethics Commission of Ningbo NO.6 Hospital, China. Written informed consent to participate in the study was obtained from all subjects before enrolment. Competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding This work was supported by Agricultural and social development science and technology project of Yinzhou District in Ningbo(No.2020AS0074),Natural Science Foundation of Ningbo City (No.202003N4299),Medical Science and Technology Project of Zhejiang Province (No.2025KY1485,2023KY1148), Ningbo Clinical Research Center for Orthopedics, Sports Medicine & Rehabilitation (No.2024L004) Author Contribution Nanjian Xu: Writing – original draft. Weihu Ma: Conceptualization, Methodology. Guanyi Liu: Supervision, Writing – review & editing. Renhai Feng: Data curation, Software. Data Availability The data that support the findings of this study are available from the corresponding author upon reasonable request. Nanjian Xu had full access to all of the data in this study and takes complete responsibility for the integrity of the data and the accuracy of the data analysis. References Grob D. Posterior occipitocervical fusion in rheumatoid arthritis and other instabilities[J]. Journal of orthopaedic science, 2000, 5(1): 82–87. Yan W, Zhou X, Zhang Y, Li J, Jia L, Yuan W. Anatomical study of posterior atlantoaxial screw fixation[J]. Chinese Journal of Orthopaedics, 2006, 26(1): 35–38. DOI: 10.3760/j.issn:0253-2352.2006.01.008 . Ma W, Wang Y, Lou Z, Xu D, Li G, Ruan C, Zhao H. Finite element analysis of occipital condyle screw fixation for upper cervical instability[J]. Chinese Journal of Traumatology, 2018, 34(4): 305–311. DOI: 10.3760/cma.j.issn.1001-8050.2018.04.004 . Anderson PA, Oza AL, Puschak TJ, et al. Biomechanics of occipitocervical fixation[J]. Spine, 2006, 31(7): 755–761. Yan W, Zhang C, Zhou X, et al. Safe angle scope for posterior atlanto-occipital transarticular screw fixation[J]. Neurosurgery, 2009, 65(3): 499–504. .Harms J, Melcher RP. Posterior C1–C2 fusion with polyaxial screw and rod fixation[J]. Spine, 2001, 26(22): 2467–2471. Donnellan MB, Sergides IG, Sears WR. Atlantoaxial stabilization using multiaxial C-1 posterior arch screws[J]. Journal of Neurosurgery: Spine, 2008, 9(6): 522–527. Resnick DK, Lapsiwala S, Trost GR. Anatomic suitability of the C1-C2 complex for pedicle screw fixation[J]. Spine, 2002, 27(14): 1494–1498. Puttlitz CM, Goel VK, Traynelis VC, et al. A finite element investigation of upper cervical instrumentation[J]. Spine, 2001, 26(22): 2449–2455. Zhang BC, Liu HB, Cai XH, et al. Biomechanical comparison of modified TARP technique versus modified Goel technique for the treatment of basilar invagination: a finite element analysis[J]. Spine, 2016, 41(8): E459-E466. Takigawa T, Simon P, Orías AAE, et al. Biomechanical comparison of occiput-C1–C2 fixation techniques: C0–C1 transarticular screw and direct occiput condyle screw[J]. Spine, 2012, 37(12): E696-E701. Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8711284","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":589886127,"identity":"30046eb0-3ec1-4620-b9fc-d940947f230a","order_by":0,"name":"Nanjian Xu","email":"","orcid":"","institution":"Ningbo No.6 Hospital","correspondingAuthor":false,"prefix":"","firstName":"Nanjian","middleName":"","lastName":"Xu","suffix":""},{"id":589886128,"identity":"1cc84191-9001-4180-bba8-c0454b6a0f6c","order_by":1,"name":"Weihu Ma","email":"","orcid":"","institution":"Ningbo No.6 Hospital","correspondingAuthor":false,"prefix":"","firstName":"Weihu","middleName":"","lastName":"Ma","suffix":""},{"id":589886129,"identity":"67823f42-e212-47dd-bc94-98c328869714","order_by":2,"name":"Guanyi Liu","email":"","orcid":"","institution":"Ningbo No.6 Hospital","correspondingAuthor":false,"prefix":"","firstName":"Guanyi","middleName":"","lastName":"Liu","suffix":""},{"id":589886130,"identity":"7fb144fe-a1a2-438f-a862-0f990103a1bf","order_by":3,"name":"Renhai Feng","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIie3RsarCMBSA4SOFI0LUNVKJr1AIZNVHaRA6XcExg0MFSQcrrn0MR0dFqMtx76hvcN3cvBeum2J6N4d8c35OTgLgeR8Im/N0921QDI/r6zk2M3fSYYf9paCOBNrJ6EylOxE8GcuWFTqtRqp3WQQ1LsZIhUBKNgpIjE4RutkyduySq3BqEhGEaVnpbR84nTbuKQWVEvt7W2lCiPjEkfAvFbbtXed8jFNtgzrJ7/pti7rgCUK95O+RUUaMAh5TyZy7DLLHV0bNvHG9mZnoZqv3yRP2v+Oe53neSz+3W0w5Q66jlwAAAABJRU5ErkJggg==","orcid":"","institution":"Ningbo No.6 Hospital","correspondingAuthor":true,"prefix":"","firstName":"Renhai","middleName":"","lastName":"Feng","suffix":""}],"badges":[],"createdAt":"2026-01-27 13:56:58","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8711284/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8711284/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102828923,"identity":"cfd13353-44eb-4226-95ac-02483f408a8e","added_by":"auto","created_at":"2026-02-17 09:26:45","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":207724,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of four finite element models of atlantoaxial internal fixation A. Occipital condyle screw + C1 lateral mass screw+ C2 pedicle screw fixation model; B. Occipital plate screw + C1 lateral mass screw+ C2 pedicle screw fixation model; C. Transarticular screw + C2 pedicle screw fixation model at C1-C2 joint; D. AO-CO-C screw + C2 pedicle screw fixation model\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8711284/v1/01c8ad6b434c613bb591c01e.jpeg"},{"id":102828945,"identity":"39df25cb-6b51-4b75-bde9-2c9d30a5fc2a","added_by":"auto","created_at":"2026-02-17 09:26:50","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":195360,"visible":true,"origin":"","legend":"\u003cp\u003eShows stress cloud diagrams of four types of internal fixation on the atlantoaxial joint. Colors changing from blue to green to yellow to red indicate increasing stress, with “MAX” indicating the peak stress position. Models A-D depict flexion, extension, lateral bending, and rotation conditions fixed by occipital condyle screw + C1 lateral mass + C2 pedicle screw; models E-H depict similar conditions fixed by occipital plate screw + C1 lateral mass + C2 pedicle screw; models I-L depict conditions fixed by transarticular screw + C2 pedicle screw; models M-P depict conditions fixed by AO-CO-C screw + C2 pedicle screw.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8711284/v1/26cdb53d7d04295c3e1467bb.jpeg"},{"id":102828862,"identity":"45b45fe7-7d56-4252-bdbd-3c49b3cdd526","added_by":"auto","created_at":"2026-02-17 09:26:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":117454,"visible":true,"origin":"","legend":"\u003cp\u003eModel of unstable neck and four types of internal fixation models for flexion, extension, lateral bending, and rotation of ROM.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8711284/v1/e86750f56ff617b27643ffb3.png"},{"id":103056498,"identity":"aa30fb64-493d-4704-95d2-7d0f7d63e858","added_by":"auto","created_at":"2026-02-20 09:12:07","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1128160,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8711284/v1/89f818a2-5d6d-4e60-92ed-29610cb27eab.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Biomechanical finite element analysis of occipitocervical joint-zonular bone-occipital condyle-screw on the inclined plane","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe junction between the occiput and the cervical spine is different in anatomy and function from the lower cervical vertebrae\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e. It is the most flexible segment of the cervical spine. Trauma, tumors, congenital malformations, and inflammation can all cause instability in the occipitocervical junction. Posterior occipitocervical fixation and fusion are commonly used to treat occipitocervical instability with good outcomes. Posterior occipitocervical fixation includes occipital and cervical side fixation. There are various techniques for cervical side screw placement, which provide reliable fixation. However, the anchoring points on the occipital side are limited to the occipital squama and occipital condyles. The occipital bone plate and screw system is currently the mainstream method for posterior occipitocervical fusion surgery, but factors such as the thickness of the occipital squama bone, the rich vascular network in the inner plate region of the occipital squama, can affect the fixation effectiveness and surgical risks. Additionally, for patients with partial occipital bone loss or severe osteoporosis after decompression surgery, occipital condyle screws can be used as an alternative. However, there are doubts about the possibility and stability of screw placement when patients also have congenital malformations. Some scholars have proposed the effectiveness of occipitocervical screw fixation through the atlantooccipital joint\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. However, biomechanical studies on cadaver specimens have shown that screw fixation through the atlantooccipital joint combined with occipital bone plate fixation may be slightly inadequate in stability\u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e. In 2021, our team designed and proposed the technique of posterior atlantooccipital joint-occipital condyle-slope screw fixation (AO-CO-C screws), with longer screw paths that traverse more cortical bone. The stability of the structure cannot be solely explained by the range of motion (ROM) limitations obtained from cadaver-based biomechanical studies. To understand the stability of the structure, it is necessary to study the stresses acting within the metal structure and utilize finite element models (FEMs) for analysis. In three-dimensional finite element models, various types of posterior occipitocervical fixation can be biomechanically tested and stresses can be compared within the instruments. Currently, there is limited research on posterior occipitocervical fixation using finite element methods. Therefore, this study intends to use the finite element method to analyze the influence of AO-CO-C screws on the biomechanical stability of C0-C2 and provide a theoretical basis for selecting surgical methods for occipitocervical instability.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Finite Element Model Establishment\u003c/h2\u003e \u003cp\u003eSeparate normal C0-C2 finite element model, atlantoaxial instability finite element model, atlantoaxial fusion with C1 lateral mass screw and C2 pedicle screw fixation finite element model (Group A), occipital plate screw with C1 lateral mass screw and C2 pedicle screw fixation finite element model (Group B), transarticular atlantoaxial screw with C2 pedicle screw fixation finite element model (Group C), occipital-cervical screw with counter-odontoid peg-C2 pedicle screw fixation finite element model (Group D). (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e \u003ch2\u003e2.1.1 Establishment of Normal C0-C2 Finite Element Model\u003c/h2\u003e \u003cp\u003eApproved by the hospital\u0026rsquo;s ethics committee. Utilizing cervical spine CT imaging data of a 27-year-old female with no prior history of occipito-cervical diseases or traumatic fractures. DICOM data was imported into Mimics 21.0 software (Materialise, Belgium) to initially create corresponding 3D mesh models and export bone STL format model data files. Further processing was done using Geomagic 2017 software (Geomagic, USA) for surface optimization and feature modeling of cortical and cancellous bone, followed by assembly in SolidWorks 2017 (Dassault Syst\u0026egrave;mes, France) to simulate the normal state, and finally imported into Ansys 17.0 software (Ansys, USA) to establish the complete model. We performed a mesh convergence study to determine the optimal mesh size for both the instrumentation and the pelvis model. The study involved progressively refining the mesh and analyzing the resulting changes in deformation and stress values. The results demonstrated that a mesh size of 0.9mm provided stable and accurate results without significant changes in the outcomes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.1.2 Establishment of Atlantoaxial Instability Finite Element Model\u003c/h2\u003e \u003cp\u003eBuilding upon the normal C0-C2 finite element model, the atlantoaxial instability finite element model was created by eliminating the transverse ligament, alar ligament, and apical ligament using SolidWorks 2017 (Dassault Syst\u0026egrave;mes, France).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.1.3 Establishment of Finite Element Models for Four Atlantoaxial Posterior Fixation Devices\u003c/h2\u003e \u003cp\u003eFour models of atlantoaxial posterior fixation devices were designed using SolidWorks 2017 (Dassault Syst\u0026egrave;mes, France), adjusting spatial positions and aligning them with the aforementioned atlantoaxial instability finite element model to create the finite element models for occipital fusion screw with C1 lateral mass screw and C2 pedicle screw fixation, occipital plate screw with C1 lateral mass screw and C2 pedicle screw fixation, transarticular atlantoaxial screw with C2 pedicle screw fixation, and AO-CO-C screw with C2 pedicle screw fixation. The fixation segments mentioned above are all in the C0-C2 region. The occipital fusion screw is inserted 2mm above the atlantoaxial joint, 5mm outward from the inner edge of the occipital condyle, with an inward angle of 22\u0026deg;and a head angle of 5\u0026deg;. The occipital steel plate screw fixation position is based on the method of Anderson et al. \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e, the transarticular atlantoaxial screw fixation position is based on Yan et al\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e., and the atlantoaxial lateral mass screw and pedicle screw fixation is based on the method of Harms and Melher\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Material properties, boundary conditions, and load conditions\u003c/h2\u003e \u003cp\u003eIn Mimics software, material parameters are assigned to bones and implants based on the material parameter table, with screws and rods made of Ti-6A14V titanium alloy. We simulated the screws using a simplified cylindrical design. This choice was made to simplify computational load and focus on overall stability analysis. Ligaments are assigned values based on load-deformation curves, with specific ligament properties shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e \u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. The motion of the bottom surface of C2 is restricted, and the contact characteristics between joints involve frictionless surface-to-surface contact. A vertical load of 40 N and a lateral bending, extension, and rotation moment of 1.5 N\u0026sdot;m are incrementally applied to the upper surface of C0 to simulate the gravitational load on the head and the flexion, extension, lateral bending, and rotational movements of C0-C2 \u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e. This study neglects the micro-motions between bones and screws, defining the contact between screws and surrounding bones as bonded contact. We used [tetrahedral(Solid186)] elements to model the bones and instrumentation in our finite element analysis. These elements were chosen for their suitability in capturing the complex geometry of the structures involved, particularly in relation to the bending and loading conditions applied in our study.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMaterial Properties Table\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterials\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eElastic modulus\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePoisson\u0026rsquo;s ratio\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCortical bone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e11000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTrabecular bone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eArticular cartilage\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnterior longitudinal ligament (C0-2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnterior atlantoaxial membrane (C0-1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWorld behind the pillow (C0-1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSharp pointed ligament between teeth (C0-1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e38(1.88)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWing-shaped ligament\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e23(1.14)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCruciate ligament\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e16(0.79)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCovering membrane (C0-2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e27(1.34)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnterior cruciate ligament (C1-2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e58(2.88)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePosterior cruciate ligament (C1-2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e63(3.13)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eJoint capsule\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e176(8.73)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNuchal ligament\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e208(10.32)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInternal fixation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e180(8.93)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Observation indicators\u003c/h2\u003e \u003cp\u003eCompare the range of motion (ROM) of each model under different operating conditions to evaluate its stability; observe stress distribution cloud maps of four internal fixation devices after reaching static equilibrium under different conditions, and compare stress peak values and stress distribution characteristics.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Validation of the complete finite element method\u003c/h2\u003e \u003cp\u003eIn order to validate the finite element model, the range of motion (ROM) of the complete C0-C2 model was calculated and compared with the in vitro study by Takigawa T \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e. The ROM of the complete C0-C2 model is as follows: flexion/extension 29.5\u0026deg;\u0026plusmn;11.1\u0026deg;, lateral bending 4.3\u0026deg;\u0026plusmn; 4.6\u0026deg;, rotation 62.3\u0026deg;\u0026plusmn;13.0\u0026deg;. The ROM data from previous literature are very consistent with our research results. (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of the ROM of the complete C0-2 model with the reference literature\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eForward bend\u0026thinsp;+\u0026thinsp;backward stretch\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eSide bend\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eRotation\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTomoyuki Takigawa etc.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eThis study\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTomoyuki Takigawa etc.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eThis study\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTomoyuki Takigawa etc.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eThis study\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC0-C2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e29.5\u0026deg;\u0026plusmn;11.1\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29.33\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e4.3\u0026deg;\u0026plusmn;4.6\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e11.6\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e62.3\u0026deg;\u0026plusmn;13.0\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e25.11\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Internal fixation stress distribution\u003c/h2\u003e \u003cp\u003eAccording to the screw fixation method of each type of internal fixation device, stress peaks inside the screws were observed at different locations (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The internal fixation stress peak of Group A is located in the region where the occipital condyle screw first contacts the occipital condyle bone. Stress peaks in the internal fixations of Groups C and D appear in the atlanto-occipital joint region. The stress peak of internal fixation Group B is located at the base of the lateral mass screw of C1 (i.e., the middle section of the entire fixation device). Group D\u0026rsquo;s internal fixation has the lowest stress peak in flexion conditions but has a higher stress peak in extension conditions; under lateral bending and rotation conditions, the stress peak is between the four types of internal fixation devices. In extension and lateral bending conditions, the internal fixation stress peaks of Groups A and B are lower than Groups C and D. In rotation conditions, the internal fixation stress peaks of Groups C and D are lower than Groups A and B. (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn forward bending, backward stretching, lateral bending, and rotation conditions, compared with the unstable cervical spine model, the ROM of the four groups of models all decreased by 80% (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In Group A, ROM decreased by 89.6%, 92.2%, 88.4%, and 86.0% in forward bending, backward stretching, lateral bending, and rotation conditions, respectively. Group B saw a decrease of 82.4%, 93.6%, 86.7%, and 84.3% in forward bending, backward stretching, lateral bending, and rotation conditions, respectively. Group C experienced reductions of 89.2%, 91.8%, 87.4%, and 85.5% in forward bending, backward stretching, lateral bending, and rotation conditions, respectively. Group D showed decreases of 89.2%, 90.0%, 92.0%, and 90.9% in forward bending, backward stretching, lateral bending, and rotation conditions, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eCurrently, occipitocervical fixation and fusion are widely used in the treatment of occipitocervical instability. Some scholars \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e have compared the biomechanics of various occipitocervical fixation techniques using range of motion (ROM) data in in vitro studies. However, due to the nature of cadaveric studies, each cadaveric model may have structural variations. Additionally, if experiments are conducted under different conditions for each model, the models themselves may deform, thus affecting the ROM data. In the case of finite element analysis, stress concentrations on the instrument can be measured without deformation of the model through repeated tests. In finite element analysis studies of occipitocervical fixation, there is still a lack of comparative research on four different fixation techniques. This study found that in flexion and extension conditions, Group C had higher stress peak values than Groups A and B, further confirming the inadequacy of stability in flexion and extension with occipitocervical screws. Compared to Group C, the stress peak values in Group D decreased significantly, especially in flexion conditions, even lower than Groups A and B. This indicates that compared to occipitocervical joint screws, AO-CO-C screws not only lengthen the trajectory but more importantly enhance stability. Our preliminary study found that the head inclination angle of AO-CO-C screws is approximately 50\u0026deg;, with an inward angle of about 18\u0026deg;, allowing the screw head to reach the front edge of the slope, crossing the center of gravity of the skull, providing effective support to the forehead. In addition, the direction of AO-CO-C screws is closer to the vertical plane, allowing the vector of skull gravity to be conducted along the long axis of the screw, and the 50mm lever arm is equivalent to the longitudinal connecting rod of occipital screws, compensating for the instability of occipitocervical screws in flexion and extension. In lateral bending conditions, the internal fixation stress peak values in Groups A and B are lower than in Groups C and D. In rotational conditions, the internal fixation stress peak values in Groups C and D are lower than in Groups A and B, but Group D is higher than Group C. This indicates that extending the lever arm can improve the rotational stability of internal fixation, but the impact of screws passing through the occipitocervical joint on rotational stability is more important. In addition, the addition of a cross-connecting rod during surgery can further enhance the rotational stability of AO-CO-C screws. The rigidity of the screws themselves, the length of the screw trajectory during insertion, and the number of cortical bone perforations are all important factors affecting the biomechanical stability of screws. Takigawa T et al. \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e believe that occipitocervical screws are too short to support the weight of the forehead and that patients with severe occipitocervical instability may still need additional anterior fixation. Yan Wangjun et al. \u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e found that the trajectory length of occipitocervical screws is about 30mm, whereas the trajectory within the occipital condyle is even shorter. As a new occipitocervical internal fixation technique, AO-CO-C screws can achieve a trajectory length of over 50mm, providing a larger screw-bone contact interface compared to other screws. Additionally, in different fixation methods, stress peak values occur at different locations. The internal fixation stress peak of occipital condyle screws is in the region where the screw first contacts the occipital condyle bone. The internal fixation stress peak of occipital plate screws appears in the base area of the C1 lateral mass screw (i.e., the middle section of the entire fixation device). The internal fixation stress peaks of occipitocervical joint screws and AO-CO-C screws both occur in the occipitocervical joint region. AO-CO-C screws can penetrate through 2 layers of joint surface\u0026thinsp;+\u0026thinsp;3 layers of cortical bone under the slope, far exceeding the 1 layer of cortical bone of occipital condyle screws and the 3 layers of cortical bone of posterior occipitocervical joint screws. For patients with severe osteoporosis or partial bone loss in the occipital region, AO-CO-C screws can provide greater resistance to screw pullout and reduce the failure rate of internal fixation. Therefore, based on the ROM, stress peak values, and stress distribution of each fixation device in this study, the structure of AO-CO-C screws is the most stable. Our study has several limitations. First, in finite element analysis, it is assumed that the screw is in full contact and fixed with the bone, which is not always achieved in clinical practice. Therefore, in the finite element model, this rigid bone-metal interface emphasizes the decrease in ROM after fixation. Our study analyzed the biomechanics of the occipitocervical region based on screw fixation, without considering bone fusion. Additionally, the impact of bone fusion on the stability of the occipitocervical region is not yet clear. To enhance the stability of the occipitocervical structure, we recommend increasing interbody bone grafts to improve stability.\u003c/p\u003e \u003cp\u003eIn conclusion, this study compared the biomechanical stability of four occipitocervical fixation techniques, which can help spine surgeons choose the appropriate surgical technique. For the strongest occipitocervical joint stability, this study recommends AO-CO-C fixation. If other fixation methods were chosen, we suggested increasing the duration of cervical support fixation postoperatively, closely monitoring and paying attention to the maximum stress points of the screw in imaging examinations (X-ray and CT scans), including screw loosening, screw-bone interface fractures, or screw fractures.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eAO-CO-C screws\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eatlantooccipital joint-occipital condyle-slope screw fixation\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eFEM\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003efinite element model, ROM=range of motion, CT=computed tomography\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":" \u003ch2\u003eEthics approval and consent to participate\u003c/h2\u003e \u003cp\u003eThe study was performed in accordance with the Declaration of Helsinki and was reviewed and approved by the Ethics Commission of Ningbo NO.6 Hospital, China. Written informed consent to participate in the study was obtained from all subjects before enrolment.\u003c/p\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was supported by Agricultural and social development science and technology project of Yinzhou District in Ningbo(No.2020AS0074),Natural Science Foundation of Ningbo City (No.202003N4299),Medical Science and Technology Project of Zhejiang Province (No.2025KY1485,2023KY1148), Ningbo Clinical Research Center for Orthopedics, Sports Medicine \u0026amp; Rehabilitation (No.2024L004)\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eNanjian Xu: Writing \u0026ndash; original draft. Weihu Ma: Conceptualization, Methodology. Guanyi Liu: Supervision, Writing \u0026ndash; review \u0026amp; editing. Renhai Feng: Data curation, Software.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request. Nanjian Xu had full access to all of the data in this study and takes complete responsibility for the integrity of the data and the accuracy of the data analysis.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGrob D. Posterior occipitocervical fusion in rheumatoid arthritis and other instabilities[J]. Journal of orthopaedic science, 2000, 5(1): 82\u0026ndash;87.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYan W, Zhou X, Zhang Y, Li J, Jia L, Yuan W. Anatomical study of posterior atlantoaxial screw fixation[J]. Chinese Journal of Orthopaedics, 2006, 26(1): 35\u0026ndash;38. DOI: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3760/j.issn:0253-2352.2006.01.008\u003c/span\u003e\u003cspan address=\"10.3760/j.issn:0253-2352.2006.01.008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMa W, Wang Y, Lou Z, Xu D, Li G, Ruan C, Zhao H. Finite element analysis of occipital condyle screw fixation for upper cervical instability[J]. Chinese Journal of Traumatology, 2018, 34(4): 305\u0026ndash;311. DOI: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3760/cma.j.issn.1001-8050.2018.04.004\u003c/span\u003e\u003cspan address=\"10.3760/cma.j.issn.1001-8050.2018.04.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnderson PA, Oza AL, Puschak TJ, et al. Biomechanics of occipitocervical fixation[J]. Spine, 2006, 31(7): 755\u0026ndash;761.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYan W, Zhang C, Zhou X, et al. Safe angle scope for posterior atlanto-occipital transarticular screw fixation[J]. Neurosurgery, 2009, 65(3): 499\u0026ndash;504.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e.Harms J, Melcher RP. Posterior C1\u0026ndash;C2 fusion with polyaxial screw and rod fixation[J]. Spine, 2001, 26(22): 2467\u0026ndash;2471.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDonnellan MB, Sergides IG, Sears WR. Atlantoaxial stabilization using multiaxial C-1 posterior arch screws[J]. Journal of Neurosurgery: Spine, 2008, 9(6): 522\u0026ndash;527.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eResnick DK, Lapsiwala S, Trost GR. Anatomic suitability of the C1-C2 complex for pedicle screw fixation[J]. Spine, 2002, 27(14): 1494\u0026ndash;1498.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePuttlitz CM, Goel VK, Traynelis VC, et al. A finite element investigation of upper cervical instrumentation[J]. Spine, 2001, 26(22): 2449\u0026ndash;2455.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang BC, Liu HB, Cai XH, et al. Biomechanical comparison of modified TARP technique versus modified Goel technique for the treatment of basilar invagination: a finite element analysis[J]. Spine, 2016, 41(8): E459-E466.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTakigawa T, Simon P, Or\u0026iacute;as AAE, et al. Biomechanical comparison of occiput-C1\u0026ndash;C2 fixation techniques: C0\u0026ndash;C1 transarticular screw and direct occiput condyle screw[J]. Spine, 2012, 37(12): E696-E701.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-medical-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ejmr","sideBox":"Learn more about [European Journal of Medical Research](http://eurjmedres.biomedcentral.com)","snPcode":"40001","submissionUrl":"https://submission.nature.com/new-submission/40001/3","title":"European Journal of Medical Research","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"biomechanical finite element analysis, screw fixation, cervical spine","lastPublishedDoi":"10.21203/rs.3.rs-8711284/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8711284/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003eThis study aimed to determine the biomechanical stability of C0-C2 vertebrae fixed by atlantooccipital joint-occipital condyle-slope screw fixation (AO-CO-C screws) using finite element analysis.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eUsing computed tomography images, a nonlinear intact three-dimensional C0-2 finite element model (FEM) was developed and validated. Six FEMs were reconstructed: intact model, unstable model, atlantoaxial fusion with C1 lateral mass screw and C2 pedicle screw fixation finite element model (Group A), occipital plate screw with C1 lateral mass screw and C2 pedicle screw fixation finite element model (Group B), transarticular atlantoaxial screw with C2 pedicle screw fixation finite element model (Group C), occipital-cervical screw with counter-odontoid peg-C2 pedicle screw fixation finite element model (Group D). Range of motion and maximum von Mises stresses were compared under flexion, extension, lateral bending, and axial rotation.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eGroup D showed the greatest decrease in ROM(range of motion) with flexion, which was higher than that of the other techniques. The maximal von Mises stress on Group A and Group B showed the occipital condyle screw began contact with the occipital condyle bone, whereas Group C and Group D. Group C had maximal von Mises stress on the atlanto-occipital joint region; the maximal von Mises stress on Group A was located in the area where the occipital condyle screw began contact with the occipital condyle bone, whereas Group C and Group D had maximal von Mises stress on the atlanto-occipital joint region, and the maximal von Mises stress on Group B was located in the area of the bottom of the C1 lateral mass screw.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eIn this study, AO-CO-C screws fixation is the most stable technique. If surgeons have to use other fixation methods, they should be aware that additional fixation or postoperative immobilization may be required to achieve ROM restriction. Careful observation at the maximum stress site on the screw, including screw loosening, screw-bone interface disruption, or screw fracture, is necessary during follow-up imaging examinations(X-ray and CT scans)after occipitocervical posterior fixation.\u003c/p\u003e","manuscriptTitle":"Biomechanical finite element analysis of occipitocervical joint-zonular bone-occipital condyle-screw on the inclined plane","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-17 09:23:57","doi":"10.21203/rs.3.rs-8711284/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-04-20T14:28:28+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-17T11:55:16+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-15T09:16:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-08T14:10:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"214918156793227769600478995086252948761","date":"2026-03-30T15:03:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"166860815897079033784434371445109991545","date":"2026-03-28T06:48:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"288984436977329739295798263916013748055","date":"2026-03-27T18:41:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"321907731008517039500516318691562673890","date":"2026-03-27T14:45:58+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-11T09:00:52+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-04T10:31:10+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-04T10:26:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"European Journal of Medical Research","date":"2026-01-27T13:40:23+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-medical-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ejmr","sideBox":"Learn more about [European Journal of Medical Research](http://eurjmedres.biomedcentral.com)","snPcode":"40001","submissionUrl":"https://submission.nature.com/new-submission/40001/3","title":"European Journal of Medical Research","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"747ac233-015b-47d2-9f8c-beb37bbf92ae","owner":[],"postedDate":"February 17th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-02-17T09:23:57+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-17 09:23:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8711284","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8711284","identity":"rs-8711284","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}